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Appendix Physical Chemistry

Physical Quantities:

In physical science, we commonly deal with quantities such as pressure, volume, mass, temperature, current, etc. These quantities are known as physical quantities. A physical quantity has two components, namely, numerical value and its unit and is written as

  • Physical quantity = (Numerical value)(unit)
    Examples : Force = 5 Newton Here Physical Quantity is Force and its Numerical value 5 and units Newton.

  • 1. C.G.S. Units:
    Physical Quantity  Name of Unit  Symbol 
    Length  Centimeter  cm
    Mass  Gram  gm
    Time  Second → s
    Electric current  Ampere  amp
    Temperature  Kelvin  °K

  • 1. S.I. Units:
    Physical Quantity  Name of Unit  Symbol
    Length  Meter  m
    Mass  Kilogram  Kg
    Time  Second  s
    Electric current  Ampere  amp
    Temperature  Kelvin  °K

  • Dimension of Physical Quantity:
    Dimension of Mass = M
    Dimension of Length = L
    Dimension of Time = T

  • Derived Units and Dimension From its Basic Formula:
  • Area:

    Area = Length × Length
    Thus the unit of Area = Unit of Length × Unit of Length
    Unit of Area in C.G.S. System is cm²
    Unit of Area in S.I. System is

     

  • 1. Force:
From the Newton Second Low of Motion,
Force = Mass × Acelaration
or, Force = Mass × Velocity/Time
or, Force = Mass × (Length/Time) /Time
or, Force = Mass × (Length/Time²)
Thus the unit of Force in C.G.S. System,
= Unit of Mass × (Unit of Length/Unit of Time²)
= gram × (cm/sec²)
= gram cm/sec² or gram cm sec⁻²
or Dyne
Again in the same way Unit of Force in S.I System,
= Kg m/sec² or Kg m sec⁻²
or Newton
From the above discussion dimension of Force,
= dimension of Mass × (dimension of Length/dimension of Time²)
Thus the dimension of Force = [T⁻²]

  • Conservation of 1 Newton to 1 Dyne :
1 Newton = 1 Kg m/sec²
= (1Kg × 1 m )/1 sec²
We know that, 1 Kg = 10³gm and 1 m = 10² cm
Thus, 1 Newton = (10³gm × 10² cm)/1 sec²
= 10⁵ gram cm/sec²
= 10⁵ Dyne
  • 2. Work:
We Know that,
Work (W) = Force(F) × Displacement(d)
Thus, the unit Work = unit of Force × unit of Displacement(d)
So the Unit of Work in C.G.S. System,
= (gram cm/sec²) × cm 
or gram cm²/sec² gram cm² sec⁻²
or erg
And the unit of work in S.I. system,
or Kg m²/sec² Kg m² sec⁻²
or Joule

From the above discussion dimension of Work,
= dimension of Mass × {(dimension of Length)²/dimension of Time²}
Thus the dimension of Work = [L² T⁻²]

  • Conservation of 1 Joule to 1 erg :

1 Joule = 1 Kg m²/sec²
= (1Kg × 1 m² )/1 sec²
We know that, 1 Kg = 10³gm and 1 m = 10² cm
Thus, 1 Joule = {10³gm × (10²)² cm}/1 sec²
= 10⁷ gram cm²/sec²
= 10⁷ erg
  • Energy :
The ability to doing work is termed as Energy.
Thus, the unit and dimension of energy and work is same.
Unit of Energy in C.G.S System is erg and S.I. System is Joule.